1. Field of the Invention
Embodiments of the present invention generally relate to baghouse filter systems and the tube sheets used thereby. More particularly, embodiments of the present invention relate to the orifices within tube sheets of baghouse filter systems.
2. Description of the Related Art
Commercial baghouses of various configurations, including pulse jet, reverse air, and shaker baghouse designs, are used for removing gas-borne particulates generated in various manufacturing or industrial processes. Reverse air baghouse filter installations, operating either under positive or negative pressure configurations, are typically utilized in steel mills, cement, and limestone plants, as well as in other installations where dust collection is mandated to control air pollution.
Reverse air baghouses include numerous separately suspended filters establishing a gas or air flow passageway between an inlet volume which receives dirty gas to be filtered and a vented outlet volume for exhausting cleaner, filtered air or gas. Particulates borne by the entering gas stream are trapped and captivated by the filter bodies of the filters.
Numerous baghouse and baghouse filter designs are known. In some baghouse designs, multiple, tube-like fabric filter bags hung from J-hooks in an upper plenum provide a gas or air flow path trap to the vent system. The lower ends of the bag filters are coupled to various collars in a tube sheet floor, and gas enters the tubes through the collars.
Most baghouse filter designs include some form of header plate or cell plate, often referred to as a tube sheet, that divides and separates adjacent baghouse volumes. The tube sheet typically includes multiple circular orifices therethrough. The purpose of the tube sheet is to direct the gas flow to the inside of the filter bag via the orifices within the tube sheet, thus forcing the gas to pass through the fabric body of the filter bag.
Typically, the filter tubes are oriented vertically with respect to the air plenum. Suitable collars or attachment fixtures are coaxially associated with the orifices located in the headers or tube sheets. Various mechanical means are utilized for attaching the filter bags to the orifices; for example, with pulse jet designs, an open end of each filter bag may be attached to a venturi or collar which is fitted to each orifice. The filter bag may be attached to the venturi with a conventional encircling clamp or band and then secured to the orifice by a twist-lock design. Other attachment techniques include double-beaded snap bands and single snap bands.
Filter bags are available in several different lengths and diameters and may measure upwardly from approximately four inches in diameter and lengthwise may measure up to approximately forty feet. Given the high working temperatures to which some filters are subjected, and the various pressure-generated forces encountered during operation, some means must be provide for preventing the bags from totally collapsing during cleaning cycles. Thus, bags may be reinforced by wire cages placed within the filter bags subsequent to their hanging.
Many filter bags have tube-like, fabric exteriors that surround an inner, rigid skeleton composed of wire or metal. A secure and reliable connection prevents particulate waste from escaping the baghouse chamber.
Some designs use a rigid, self-supporting fabric. Filters having fabric formed over rigid frames are commercially known as “cartridges.” These designs are capable of collecting particulates on the outside of the fabric. Typical filter cartridges have an inner, perforated tubular sleeve coaxially surrounded by an annular filter, often comprising a resin-impregnated fabric or filter. Alternatively, air filter bags may be reinforced by a series of concentric, spaced-apart reinforcing rings disposed within their length.
Many baghouse filter systems employ tube sheets designed for twist-lock filters, the tube sheets having tabbed orifices therein which include a plurality of rigid, radially spaced apart tabs. Filter bags are coupled to a mechanical venturi or collar. The venturi or collar then twistably fits into the tabbed orifice, and the filter bag becomes locked into place when forcibly rotated within the orifice into engagement with the peripheral tabs.
Instead of the above-described twist-lock-mounted filter bags, it is often less expensive and therefore advantageous to use simpler snap-band-mounted filter bags. These designs include a deformable snap band that coaxially fits into a smoothly-rounded, tabless orifice.
Because snap-band-mounted filter bags are often more desirable than the twist-lock-mounted filter bags, and because many tube sheets are currently adapted for use with twist-lock-mounted filter bags, it would be advantageous to convert the orifices of tube sheets usable with twist-lock-mounted filter bags to orifices usable with snap-band-mounted filter bags. Unfortunately, tube sheets formed with tabbed orifices for mounting twist-lock filter bags are difficult to convert for use with snap-band-mounted filter bags. A tube sheet which is capable of mounting snap-band-mounted filter bags requires machining of very precisely-dimensioned laser-cut orifices into a metal plate with little room for error; therefore, an entirely new tube sheet with the tabbed orifices already cut therein must be installed to convert the twist-lock-type orifices to the snap-band-type orifices. Accordingly, modification of the orifices of the tube sheets is tedious and labor-intensive, often requiring gas torches to remove and replace sections and entire tube sheets and subsequent retrofitting of the converted tube sheets into place and seal welding of the converted tube sheets to the remainder of the baghouse filter system.
It is therefore advantageous to provide a machine for quickly converting tube sheet orifices of the locking-tab type to smooth, tabless orifices which are capable thereafter of receiving snap-bands for mating with less expensive filter bags and providing a better seal therebetween. It is further advantageous to provide a machine which does not require welding equipment or gas torches to effectuate the conversion of the orifices, thus eliminating the tedious and labor-intensive process of conversion described above.